diff --git a/.jules/bolt.md b/.jules/bolt.md
index 43fafef..b562ba9 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -5,3 +5,7 @@
 ## 2024-05-18 - Concurrent Fetching with Owner IDs in Share Links
 **Learning:** In the share system, endpoints processing a share code typically suffer from waterfall latency by first loading target entity details (like a project) and then querying its associated elements (like project lists) using the entity's owner ID (`userId`). However, the `shareLink` object already contains the `userId` field (representing the owner's ID).
 **Action:** Always leverage the existing owner's ID within `shareLink` to bypass sequential dependencies and fetch parent entities (like projects) concurrently with their child elements (like user lists) using `Promise.all`.
+
+## 2024-07-06 - In-Memory Derivation of Data Subsets
+**Learning:** When fetching both a global collection (e.g., all lists for a user) and a subset of that collection (e.g., lists associated with a specific project) simultaneously on the frontend, making two separate API requests causes redundant database queries and network latency.
+**Action:** Always derive the subset in-memory using array filtering (e.g., `allLists.filter(list => list.projectId === projectId)`) from the globally fetched collection, eliminating the redundant subset API request entirely.
diff --git a/src/app/projects/[id]/page.tsx b/src/app/projects/[id]/page.tsx
index 8e121a4..5c64088 100644
--- a/src/app/projects/[id]/page.tsx
+++ b/src/app/projects/[id]/page.tsx
@@ -57,18 +57,16 @@ export default function ProjectDetailPage({ params }: { params: Promise<{ id: st
     try {
       setIsLoading(true);
 
-      // OPTIMIZATION: Execute independent network requests and JSON parsing concurrently
-      // using Promise.all. This prevents a 3-step waterfall, reducing Time to First Byte
-      // (TTFB) and overall load time significantly on this detail page.
-      const [projectRes, listsRes, allListsRes] = await Promise.all([
+      // OPTIMIZATION: Instead of making separate network requests for a subset of lists
+      // (project lists) and the global collection (all lists), we only fetch the global
+      // collection. We then derive the project lists in-memory, eliminating a redundant API request.
+      const [projectRes, allListsRes] = await Promise.all([
         fetch(`/api/projects/${projectId}`),
-        fetch(`/api/projects/${projectId}/lists`),
         fetch("/api/lists"),
       ]);
 
-      const [projectResult, listsResult, allListsResult] = await Promise.all([
+      const [projectResult, allListsResult] = await Promise.all([
         projectRes.json(),
-        listsRes.json(),
         allListsRes.json(),
       ]);
 
@@ -81,12 +79,13 @@ export default function ProjectDetailPage({ params }: { params: Promise<{ id: st
       setEditName(projectResult.data.name);
       setEditDescription(projectResult.data.description || "");
 
-      if (listsResult.success) {
-        setLists(listsResult.data);
-      }
-
       if (allListsResult.success) {
-        setAllLists(allListsResult.data);
+        const allFetchedLists = allListsResult.data as List[];
+        setAllLists(allFetchedLists);
+
+        // Derive the subset of lists that belong to this project
+        const projectLists = allFetchedLists.filter((list) => list.projectId === projectId);
+        setLists(projectLists);
       }
     } catch (err) {
       console.error("Error fetching project:", err);